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Cork insulation; a complete illustrated textbook on cork insulation ...

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—<br />

CHAPTER X.<br />

DETERMINATION OF THE HEAT CONDUCTIVITY<br />

OF VARIOUS MATERIALS.*<br />

73.—Methods Employed.—It is a complicated as well as<br />

an expensive procedure to determine with any degree of<br />

accuracy the heat c<strong>on</strong>ductivity of given materials. f In spite<br />

of this fact, a great many experiments and tests have been<br />

made over a period of many years ; but in the absence of<br />

any standard in apparatus or uniformity of procedure, the<br />

results have varied so much as often to be of no real value<br />

whatever.<br />

Most comm<strong>on</strong> of the test methods employed are<br />

(a) Ice-box Method.<br />

(b) Oil-box Method.<br />

(c) Hot-air-box Method.<br />

(d) Cold-air-box Method.<br />

(e) Flat-plate (or Hot-plate) Method.<br />

74. The Ice-box Method.—The most comm<strong>on</strong> of all<br />

methods of comparing the heat insulating value of two mate-<br />

rials has been by the use of two identical cubical metal boxes<br />

covered with the materials to be tested, each filled with ice,<br />

and observing the rate at which the ice melts. Since it is<br />

difficult to keep the entire box at 32° F., even though c<strong>on</strong>-<br />

taining ice, this method may lead to inaccurate results even<br />

as a comparatk'c test of two materials. As a method of test-<br />

ing any <strong>on</strong>e material, it is far too unreliable to be of any<br />

practical value whatever.<br />

75.—The Oil-box Method.—The oil-box method of com-<br />

parative testing c<strong>on</strong>sists in covering two identical cubical<br />

*For a comprehensive treatment of heat transmissi<strong>on</strong>, c<strong>on</strong>sult "Heat Transmissi<strong>on</strong><br />

of Insulating Materials," in eleven parts, published by The American Society<br />

of Refrigerating Engineers, 37 W. 39th St., New York City. Price, $2.50.<br />

fFor a comprehensive treatment of methods to be employed in testing insulating<br />

materials, c<strong>on</strong>sult "An Investigati<strong>on</strong> of Certain Methods for Testing Heat Insulators,"<br />

by E. F. Grundhofer, The Pennsylvania State College Engineering Experiment Stati<strong>on</strong><br />

Bulletin No. 33. Price, 25 cents. Address: State College, Pa.<br />

115<br />

:

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